The invention relates to a fluid warmer and a method of operating a fluid warmer.
The application of large quantities of non-warmed fluids, for example, during the intravenous administration of blood products or infusion solutions, can have disadvantageous physiological effects, one reason for this being the associated loss of body heat.
In clinical practice, fluid warmers are therefore routinely used to pre-warm the medical fluid, which flows guided in the fluid tube, to a temperature approximating the body temperature of usually 37° Celsius.
The fluid warmers according to the design that is established on the market have one or more resistance heating elements accepting alternating voltage. The resistance heating elements are provided with a first and a second power supply conductor connection for electrically conductive connection of the resistance heating element to an alternating voltage source. A heat transfer element that is thermally conductively connected to the resistance heating element is used for heat transfer to a bag-shaped vessel that is connected to a fluid tube or constituted thereby and the fluid guided in it. The heat transfer element is frequently plate-shaped to ensure efficient heat transfer to the bag-shaped vessel.
In practice, the temperature-controlled fluids come into electrically conductive contact with the person, typically bypassing the skin resistance. Resistance heating elements powered by alternating voltage, i.e., in particular line voltage of 100 V to 240 V, can, due to capacitive coupling with other components of the fluid warmer, in particular, the heat transfer element, result in disturbances of other diagnostic or therapy devices, for example, ECG units, or also of organ structures which can be electrically stimulated, in particular, the heart. The fluid warmers used in medicine must therefore always meet the high requirements for electrical safety and the strict safety standards of the international uniform classification “CF (cardiac floating).” According to these, patient leakage currents, i.e., leakage currents conducted through a person in contact with the fluid, must not exceed a current magnitude of a total of 10 μA (microamperes) under normal conditions and 50 μA in case of a fault.
It is the object of the invention to provide a fluid warmer of the above mentioned kind with a resistance heating element for alternating voltage and a method of operating such a fluid warmer that ensure a yet higher level of patient safety.